Implantable Cardioverter Defibrillators (ICDs) are implanted in patients susceptible to cardiac tachyarrhythmias including atrial and ventricular tachycardias and atrial and ventricular fibrillation. Such devices typically provide cardioversion or defibrillation by delivering low voltage pacing pulses or high voltage shocks to the patient's heart, typically about 500–800V. The ICD operates by detecting a fast heart rate or tachyarrhythmia, upon which a battery within the device housing is coupled via an inverter to a high voltage capacitor or capacitor pair to charge the capacitors. When the capacitor reaches a desired voltage, charging is stopped and the capacitors are discharged under control of a microprocessor to provide a therapeutic shock to the patient's heart.
ICDs are contained in compact housings. Housings are typically flat bodies having parallel major surfaces, and a periphery shaped to closely contain internal components to minimize device volume. The periphery is normally formed of straight or convexly rounded segments, with any corners and edged smoothly radiused for patient comfort.
To provide communication between the device circuitry and leads that extend to a patient's heart, the housing includes a connector header. The header is a body that defines bores to receive the ends of the leads, and has electrical contacts in the bores that extend through the wall of the housing via insulated sealed feedthroughs to internal circuitry. Headers are typically formed of inert material such as epoxy, which adheres to the housing surface. Housings normally define an inlet space for the header, so that the overall housing and header shape has the desired smooth form.
In existing devices, the header is formed on one corner of the housing, so that the housing is notched at the corner, and the header fills in the notch. While effective, such an arrangement may have certain disadvantages in certain applications or circumstances. With the protruding header forming the corner of the device, it is exposed to possible damage. If the device were dropped or struck against a hard surface on the protruding header, there is a risk that the header may be damaged or dislodged. In addition, with the header typically contacting the housing at only two surfaces defining the notch, and with these two surfaces being obtusely angled with respect to each other, the housing provides only limited structural support for the header. Even in instances in which the device is not dropped, the forces generated by lead insertion, and at all other stages of manufacturing, shipping, handling, and installation, may generate unwanted stresses.
Moreover, with the electrical feed-through located at one corner of the housing, connections to internal components away from the header corner require longer conductors, increasing device volume. Also, existing devices are limited to only a single housing surface to be penetrated by feed-throughs, limiting design flexibility for internal components.
In addition, the process of molding a corner-located header is challenging. Normally, a silicone mold defining the outer surface of the header is attached to a housing, and the defined chamber is filled with epoxy. However, with the protruding header exterior defined only by the flexible silicone mold, there may be unwanted variations in the final shape, with a flush resulting surface transition between the housing and header being potentially compromised.